1. Field of the Invention
The present invention relates to an apparatus used in semiconductor processing, and more specifically, to a substrate holder to support a substrate during the performance of a process on the surface(s) of the substrate.
2. Description of the Prior Art
The surfaces of substrates are routinely subjected to various processes in the production of LSIs (large scale integrated circuits), LCDs (liquid crystal displays), and data storage disks. In the production of data storage disks in the form of hard disks, a substrate holder is typically used during processing to vertically support a circular substrate having a hole formed in its center.
FIG. 9 is a schematic front view of a conventional substrate holder 1. FIG. 10 is a schematic perspective view which illustrates the operation of substrate holder 1 shown in FIG. 9. Substrate holder 1 shown in FIGS. 9 and 10 includes a base plate 11 which is disposed vertically, and fixed support claws 12 and a movable support claw 13 provided on base plate 11.
As shown in FIGS. 9 and 10, base plate 11 is a J-shaped cut-out formed from a square plate. Four fixed support claws 12 are provided in the bottom curved portion of the J-shaped base plate (referred to below as the curved portion). Fixed support claws 12 are disposed in positional relations such that, as shown in FIGS. 9 and 10, there is symmetry of the positions of pair of a claws support with respect to a vertical line which passes through the bottom most point of the J shape (indicated in the figures as central axis 10).
Each fixed support claw 12 comprises an L-shaped member formed from a short rectangular strip which has been bent. There are cut-outs in the curved portion of base plate 11, and the fixed support claws 12 are mounted in these cut-outs, affixed to base plate 11 by a screw or other fastener. The free end or tip of each fixed support claw 12 has a V-shaped indentation such as shown in FIG. 10.
Movable support claw 13 is fixed to the top surface of base plate 11. Movable support claw 13 is formed from an elongate rectangular strip which is bent into an L shape. One end of movable support claw 13 is fixed to the top surface of base plate 11 by a screw or other suitable fastener. The free end or tip portion of movable support claw 13 is positioned on the central axis 10 and is directed downward. A V-shaped indentation is formed in the tip of support claw 13.
The operation of the conventional substrate holder will now be described. Substrate holder 1 holds a substrate 2, such as a substrate for a hard disk, which is in the shape of a circular plate having an opening 20 at its center. Substrate 2 can be fitted to and released from a transfer mechanism 4 which is provided with a substrate pickup arm 3 which holds substrate 2, during transfer as shown in FIG. 10.
As shown in FIG. 10, an opening and closing device 5 which opens and closes (i.e., raises and lowers, thereby engaging and disengaging) movable support claw 13 of substrate holder 1 is provided to be used with substrate holder 1. Opening and closing device 5 includes an opening and closing pin 51 and a displacement mechanism 52. Pin 51 is capable of causing movable support claw 13, which is made of a resilient, flexible material, to bend by displacing the tip end of movable support claw 13 upward. Note that displacement mechanism 52 is capable of moving pin 51 both horizontally (i.e., laterally) and vertically.
The case in which the substrate 2 is mounted in substrate holder 1 will now be described. Substrate pickup 3 inserts its front end in opening 20 in the center of substrate 2, raises it, and carries substrate 2 horizontally to a position close to substrate holder 1. Pin 51 of opening and closing device 5 is then moved laterally by transfer mechanism 52 and is advanced to a position below movable support claw 13 of substrate holder 1. Pin 51 is moved upward, causing movable support claw 13 to bend, as indicated by the dashed line in FIG. 9. This brings movable support claw 13 to an opened state.
Substrate pickup 3 then moves substrate 2 into alignment with base plate 11 of substrate holder 1. Substrate pickup 3 positions substrate 2 at a location which is between movable support claw 13 and fixed support claws 12. Transfer mechanism 4 then lowers substrate pickup 3, such that substrate 2 comes to rest on and is supported by fixed support claws 12.
Displacement mechanism 52 of opening and closing device 5 then lowers pin 51, such that the bending force applied to movable support claw 13 is relaxed and movable support claw 13 returns to a generally horizontal position. The tip (end) portion of movable support claw 13 comes into contact with and engages the upper edge of substrate 2. As a result, movable support claw 13 engages substrate 2 from above. Substrate pickup 3 then moves back and is taken by transfer mechanism 4 to a "standby" position (not shown) to await transfer of another substrate 2. Pin 51 also moves back and returns to a standby position.
To remove substrate 2 from substrate holder 1, the procedure described above is reversed. Displacement mechanism 52 of opening and closing device 5 moves pin 51 laterally to a position below movable support claw 13. Displacement mechanism 52 of opening and closing device 5 causes movable support claw 13 to bend upward by raising pin 51. Transfer mechanism 4 drives substrate pickup 3, and the front end of substrate pickup 3 is inserted into central opening 20 of substrate 2. Substrate pickup 3 rises and lifts up substrate 2. After lifting up substrate 2, substrate pickup 3 returns to a standby position, completing removal of substrate 2 from substrate holder 1.
A processing apparatus in which the above described substrate holder 1 can be used will now be described. FIG. 11 is a schematic plan view which shows a processing apparatus in which the substrate holder shown in FIGS. 9 and 10 may be used.
The processing apparatus shown in FIG. 11 includes a substrate transfer chamber 61 and a processing chamber 62, located adjacent to one another and separated by a gate structure 66. A substrate 2 which is to be processed is mounted on a substrate holder 1 (not shown in FIG. 11) in substrate transfer chamber 61. Substrate holder 1 on which the substrate 2 has been mounted is then moved to processing chamber 62. After processing has occurred in processing chamber 62, the processed substrate is returned to substrate transfer chamber 61, and is removed from the substrate holder.
A sputtering apparatus which produces a magnetic thin film is shown as an example of the substrate processing apparatus of FIG. 11. Two magnition sputtering sources 63 are provided inside the processing chamber 62. Each sputtering source 63 comprises a target 631 which is sputtered and a magnet structure 633 which is provided at the rear of target 631. A sputtering power supply 632 imposes a required voltage on each target 631.
Magnet structure 633 consists of a columnar central magnet 634 which is provided in the center and a ring shaped peripheral magnet 635 which surrounds central magnet 634. Magnet structure 633 establishes arcuate lines 636 of magnetic force which pass through target 631. These lines 636 of magnetic force confine a plasma near the target surface and give rise to magnetron sputtering.
Processing chamber 62 is provided with a vacuum pumping system 64 and with a gas introduction system means 65 for introducing a required plasma gas into its interior. When a voltage is imposed on target 631 by sputtering power supply 632 while a plasma supporting gas is in processing chamber 62, sputtering discharge takes place in the space adjacent to target 631, and a magnetron plasma, P, is formed on each side of the substrate.
As shown in FIG. 11, sputtering sources 63 are installed as a pair such that they are positioned on opposite sides of substrate 2 which is held by substrate holder 1. Since a magnetron plasma P is formed on each side of substrate 2, magnetron sputtering on both surfaces of substrate 2 is brought about by the pair of sputtering sources 63, and thin films are deposited simultaneously on the opposing surfaces of substrate 2.
A processing apparatus in which a substrate holder of the type described above is used must produce high quality results. For example, in order to increase the recording capacity on a substrate for an information recording medium, it is desirable to produce a uniform quality magnetic thin film over a region which extends as close as possible to the peripheral edge of the substrate.
However, with the conventional substrate holder described above, the presence of support claws 12 and 13 interferes with the ability to achieve sufficiently good-quality processing of the substrate surface(s) over an area which includes the regions close to the peripheral edge of substrate 2. Processing the surfaces of the substrate by deposition of a thin magnetic film will be used as an example to describe the aforementioned disadvantage of the prior art substrate holder.
As described above, in a conventional substrate holder of the type shown in FIG. 9, a substrate 2 is held by one movable support claw 13 and four fixed support claws 12 whose tips (i.e., ends) are formed into shallow V shapes. The peripheral edge of substrate 2 fits within and is supported by these V shaped tips.
The tip portions of support claws 12 and 13 produce "shadow regions" near the peripheral edge of substrate 2 which interfere with substrate processing. The formation of these "shadow regions" causes a reduction in the quality (i.e., uniformity) of the processing step applied near the peripheral edge of the substrate. This is because in the production of a magnetic thin film, sputtered material from target 633 is blocked by the tip portions of support claws 12 and 13. This causes a local reduction in the film thickness close to the peripheral edge in the regions where support claws 12 and 13 are present.
This reduction in the quality of the substrate surface processing due to shielding of the substrate surface is generally referred to as the "shadow effect." Given the demand for higher-density recording surfaces, shadow effects have become a problem with the type of substrate holder described above because they reduce the surface area of the substrate which may be used for accurate data storage, and hence reduce the storage capacity of the disk.
One approach to reducing the shadow effects caused by the presence of support claws on a substrate holder is to reduce the number of support claws. In this regard, in order to hold a substrate 2 such as described above vertically, it has been found satisfactory to use three support claws.
If there are four or more support claws, the fourth and additional support claws often do not contact the substrate unless they are mounted with very high precision. In this situation, the position in which the substrate is supported varies depending on which three claws contact it. Thus, if there are four or more claws, the precision and hence reproducibility of the locations where the substrate is supported is reduced. Therefore, it is preferable that the number of support claws be limited to three.
Substrate holders in which substrates are held vertically by three support claws are described in the disclosures of Japanese Utility Model Publication No. 5-23570, Japanese Laid-open Utility Model Application No. 5-94267, and Japanese Laid-open Patent Application No. 8-274142. However, in the substrate holders described in those applications, the support claw which holds the lower edge of the substrate is the tip (end) portion of a plate spring. Because of this, the place where the claw holds the lower edge is subject to change depending on the substrate's weight and the spring constant of the claw. Thus, these substrate holders have the disadvantage that it is difficult to make the substrate support positions consistent from substrate to substrate.
The support claws which contact the upper edge of a substrate and are described in the disclosures of Japanese Utility Model Publication No. 5-23570 and Japanese Laid-open Utility Model Application 5-94267, contact the substrate's edge at locations which are at an angle of 45 degrees or more relative to a horizontal line through the center of the substrate. These substrate holders have the disadvantage that there is a strong possibility of damaging the quality of the substrate surface as a result of dust particles produced by the support claws.
This is because in thin film deposition processes such as sputtering, a film is deposited not only on the surface of a substrate but also on the surfaces of the support claws. When the material deposited on the surfaces of the support claws reaches a certain thickness, it peels off or flakes because of its internal stress, thereby producing particles. Particles of the thin film are particularly liable to be caused by movement of the support claws when the substrate is inserted into and removed from the substrate holder.
When particles adhere to the surface of a substrate, they cause defects in the form of local irregularities in the film thickness. In the devices described in the disclosures of Japanese Utility Model Publication No. 5-23570 and Japanese Laid-open Utility Model Application No. 5-94267, since the support claws contact the edge of a substrate at locations which are at 45 degrees or more relative to the center of the substrate, there is the probability that dust particles produced by the supports will adhere to the surface of a substrate when they fall down, and defects of the type noted above will occur.
In the substrate holder described in the disclosure of Japanese Laid-open Patent Application No. 8-274142, support claws on the left and right contact the edge of a substrate at locations which are on a line through the center of the substrate. With this device, the probability of adhesion of dust particles is reduced. However, with this type of device, there is essentially no force pressing the substrate downward. As a result, there is a risk that the substrate will not be firmly held in the vertical axis, and thus this type of conventional substrate holder has a disadvantage because it is limited in its ability to securely hold a substrate.
What is desired is a substrate holder which can be used to process a substrate uniformly in surface regions close to the peripheral edge of the substrate, and which is capable of more securely holding a substrate than available substrate holders, without increased risk of particle contamination.